In a heat exchanger of the type to which the present invention relates a bundle of parallel tubes extends between an intake header, connected to an intake pipe, and a discharge header. In operation, a process fluid flows through the tube bundle from the intake header to the discharge header and during its passage it is heated or cooled by heat transfer through the walls of the tubes.
The fluid flow rates through the individual tubes are not uniform, but are greater in the tubes near or in line with the intake pipe, as these offer less flow resistance. It is common for the intake pipe to be connected to a side of the intake header and to extend at an angle to the axis of the tubes in the bundle and in such a configuration, there is still greater variation in the flow rates through the individual tubes.
The fluid flowing through the tubes tends to leave a deposit on them, and, if allowed to build up, reduces the efficiency of the heat exchanger. The lower the flow rate of the fluid through a tube, the higher the rate at which such a deposit can build up. The uneven flow rates therefore lead to the tubes with the lowest flow rate becoming obstructed by a deposit more rapidly than would occur with uniform flow rates across the bundle.
To prevent a build up of deposit, it has been proposed to render heat exchanger self-cleaning by inserting constantly circulating scouring projectiles or balls into the intake header to wipe the inner walls of the tubes in the bundle during their passage from the intake header to the discharge header. However, because of the non-uniform flow rate, these balls tend not to flow regularly through the tubes where the flow rate is low and if a deposit is allowed to build up in a tube between the passage of scouring balls then there is a further risk of a scouring ball being jammed in the tube.